Traditionally, the roll arrangement in known twin-wire belt presses of this kind comprises a number of wire belt guide rolls and a number of pairs of press rolls. The wire-belt guide rolls are arranged directly after the dewatering tables to provide an initial, relatively weak dewatering of the fiber suspension between the wire belts by forcing these to curve around the wire belt guide rolls, so that the wire belts are pressed under surface bearing on the wire belt rolls. (The arrangement of such wire belt guide rolls usually is called an “S-roll portion”.) The press rolls are arranged after the wire belt guide rolls to provide a final, relatively strong dewatering of the fiber suspension in that each roll pair forms a press roll nip, so that the wire belts are pressed together between the press rolls under substantially line bearing on these. Normally at least two wire belt rolls and a plurality of press rolls are needed to gradually dewater the web between the wire belts, so that there is no risk of getting a breakdown of the web.
WO 99/01609 proposes a twin-wire belt press in which a combined roll pair arranged next to the dewatering tables forms a press roll nip and forces the wire belts to curve around the rolls as well. Two rolls in the press roll arrangement can therefore be eliminated, which provides a cheaper and shorter press. A drawback of the known twin-wire belt press according to WO 99/01609, however, is that the press roll nip directly after the dewatering tables generates a relatively large flow of white water that cannot completely be removed from the web. This results in a portion of the white water flow rewetting the web.